Described herein is a set of solid phase change or hot melt ink sets comprising a plurality of inks, wherein at least one of the inks of the set comprises a fluorescence agent. The set includes a combination of ink groupings comprised of a first grouping and a second grouping that both exhibit a substantially same color under ambient light conditions and in which one of the ink groupings includes more fluorescence agent than the other ink grouping of the combination. Upon exposure to activating energy, the fluorescence agent fluoresces to cause a visible change between the appearance of the two ink groupings. A combination of particular pigment colorant and fluorescence agent enables the ink with the fluorescence agent to advantageously be a dark colored ink, such as a black ink.
A number of advantages are associated with the various embodiments described herein. For example, the inks with the fluorescence agent may be used to include security features in a printed document, including features to verify the authenticity of the document and/or to include digitally stored, machine readable or encrypted information in the document. Another advantage is represented by the possibility of printing customized security content on various forms and documents a process known as Variable Data Printing, which is enabled by digital printing of security features. This is advantageous because it makes counterfeiting very difficult because each printed document must be attempted to be copied individually. The security information may be hidden in the document until exposed to activating energy or radiation such as UV light that causes the fluorescence agent to illuminate or fluoresce. The security information can then be viewed to verify the authenticity, or can be machine read to decode digitally stored encrypted information. The security information cannot be copied with existing photocopiers. Other advantages include that the two ink groupings of a combination may be made to exhibit the substantially same color in ambient light conditions, such that the presence of hidden information cannot be detected until exposed to the activating energy to initiate fluorescence, whereby at least one of the two ink groupings of the combination changes color to render the hidden information viewable/readable. Other advantages are apparent from the description herein.